A volatile situation took shape during the afternoon of the 10th.  A unseasonably deep upper low had formed aloft over the southwest U.S., while at the same time a cold front dropped south across the state during the day.  Behind the cold front was a strong polar high pressure area. The southwest flow aloft impinged on the frontal boundary, setting the stage for very strong thunderstorm development.  Temperatures reached the low 90s over far southwest Iowa, with mid 80s over the central sections.  Dew points reached the mid 60s to the south of the front by late afternoon.  North of the front, temperatures were in the 50s during the afternoon.  The very unstable air was lifted north over the frontal boundary with explosive development during the early evening as the low level jet began to strengthen.  The airmass to the south was very unstable with lifted indices of -11 C., CAPE values of 3500 J/kg, and a freezing level of only 13,300 feet.  Hail was very widespread with the event.  During the initial convection, a super-cell moved into southwest Iowa.  This storm dropped three small tornadoes in Audubon County.  All of the tornadoes were relatively short lived and caused little damage as they were in open areas.  The main weather feature was the hail.  There were numerous reports of nickel to quarter size hail with the storms.  Th largest hail occurred with the super cell in Audubon County, with tennis ball size hail falling southwest of Audubon.  In several reports of hail of ping pong to golf ball size were received from Carroll and Guthrie Counties.  As the evening progressed, a secondary line of storms formed to the north of the developing MCS.  These formed in an east to west line across northern Iowa, producing a round of hail there.  Late in the storm life cycle, a few of the storms began to produce strong winds.  As one of the storms moved through the Des Moines area, winds of 57 MPH were measured.  Some minor damage occurred to a fast food sign.  Sixty MPH winds were reported in Marion County, while 60 to 65 MPH winds blew down power line poles in Poweshiek County.  Late in the event, as the storms moved through Hamilton County, lightening struck a storage and repair shop building in Webster City.  The building was set ablaze and was a total loss.

Hail in AUDUBON, IOWA
From 10-MAY-05 18:33:00 to 10-MAY-05 18:33:00 (CST)
Location: AUDUBON
Magnitude: 1.00 
Property damage: 2K
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 10-MAY-05 19:12:00 to 10-MAY-05 19:12:00 (CST)
Location: AUDUBON
Magnitude: 1.00 
Property damage: 2K
Reported by: TRAINED SPOTTER

Tornado in AUDUBON, IOWA
From 10-MAY-05 19:13:00 to 10-MAY-05 19:17:00 (CST)
Location: KIMBALLTON
Tornado F-scale: F0
Property damage: 2K
Reported by: TRAINED SPOTTER

Tornado tracked through open fields.

Tornado in AUDUBON, IOWA
From 10-MAY-05 19:20:00 to 10-MAY-05 19:26:00 (CST)
Location: AUDUBON
Tornado F-scale: F0
Property damage: 2K
Reported by: TRAINED SPOTTER

Tornado tracked through open fields.

Hail in AUDUBON, IOWA
From 10-MAY-05 19:38:00 to 10-MAY-05 19:38:00 (CST)
Location: AUDUBON
Magnitude: 1.00 
Property damage: 5K
Reported by: AMATEUR RADIO

Hail in GUTHRIE, IOWA
From 10-MAY-05 20:05:00 to 10-MAY-05 20:05:00 (CST)
Location: GUTHRIE CENTER
Magnitude: 1.75 
Property damage: 10K
Reported by: LAW ENFORCEMENT

Hail in CRAWFORD, IOWA
From 10-MAY-05 20:05:00 to 10-MAY-05 20:05:00 (CST)
Location: MANILLA
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Hail in GUTHRIE, IOWA
From 10-MAY-05 20:10:00 to 10-MAY-05 20:10:00 (CST)
Location: GUTHRIE CENTER ARPT
Magnitude: 1.00 
Property damage: 3K
Reported by: TRAINED SPOTTER

Hail in CARROLL, IOWA
From 10-MAY-05 20:10:00 to 10-MAY-05 20:10:00 (CST)
Location: MANNING
Magnitude: 1.75 
Property damage: 25K
Reported by: LAW ENFORCEMENT

Hail in GUTHRIE, IOWA
From 10-MAY-05 20:10:00 to 10-MAY-05 20:10:00 (CST)
Location: GUTHRIE CENTER
Magnitude: 0.75 
Reported by: AMATEUR RADIO

Hail in AUDUBON, IOWA
From 10-MAY-05 20:23:00 to 10-MAY-05 20:23:00 (CST)
Location: AUDUBON
Magnitude: 0.75 
Reported by: NWS EMPLOYEE(OFF DUTY)

Hail in POLK, IOWA
From 10-MAY-05 23:01:00 to 10-MAY-05 23:01:00 (CST)
Location: DES MOINES
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 10-MAY-05 23:02:00 to 10-MAY-05 23:02:00 (CST)
Location: AUDUBON
Magnitude: 0.88 
Property damage: 2K
Reported by: TRAINED SPOTTER

Hail in POLK, IOWA
From 10-MAY-05 23:04:00 to 10-MAY-05 23:04:00 (CST)
Location: DES MOINES
Magnitude: 1.00 
Property damage: 5K
Reported by: AMATEUR RADIO

Hail in WARREN, IOWA
From 10-MAY-05 23:05:00 to 10-MAY-05 23:05:00 (CST)
Location: BEVINGTON
Magnitude: 0.75 
Reported by: LAW ENFORCEMENT

Hail in CASS, IOWA
From 10-MAY-05 23:11:00 to 10-MAY-05 23:11:00 (CST)
Location: ATLANTIC ARPT
Magnitude: 1.00 
Property damage: 3K
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 10-MAY-05 23:15:00 to 10-MAY-05 23:15:00 (CST)
Location: AUDUBON
Magnitude: 1.00 
Property damage: 3K
Reported by: EMERGENCY MANAGER

Hail in WARREN, IOWA
From 10-MAY-05 23:23:00 to 10-MAY-05 23:23:00 (CST)
Location: ST MARYS
Magnitude: 0.75 
Reported by: LAW ENFORCEMENT

Hail in JASPER, IOWA
From 10-MAY-05 23:55:00 to 10-MAY-05 23:55:00 (CST)
Location: NEWTON
Magnitude: 0.88 
Property damage: 3K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in MARION, IOWA
From 11-MAY-05 00:00:00 to 11-MAY-05 00:00:00 (CST)
Location: HARVEY
Magnitude: 52 EG
Property damage: 2K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in POWESHIEK, IOWA
From 11-MAY-05 00:30:00 to 11-MAY-05 00:30:00 (CST)
Location: GRINNELL
Magnitude: 54 EG
Property damage: 10K
Reported by: EMERGENCY MANAGER

Hail in DALLAS, IOWA
From 10-MAY-05 21:53:00 to 10-MAY-05 21:53:00 (CST)
Location: DE SOTO
Magnitude: 0.88 
Property damage: 2K
Reported by: TRAINED SPOTTER

Hail in WORTH, IOWA
From 10-MAY-05 21:55:00 to 10-MAY-05 21:55:00 (CST)
Location: FERTILE
Magnitude: 1.00 
Property damage: 3K
Reported by: GENERAL PUBLIC

Hail in AUDUBON, IOWA
From 10-MAY-05 22:00:00 to 10-MAY-05 22:00:00 (CST)
Location: KIMBALLTON
Magnitude: 1.50 
Property damage: 10K
Reported by: TRAINED SPOTTER

Hail in DALLAS, IOWA
From 10-MAY-05 22:02:00 to 10-MAY-05 22:02:00 (CST)
Location: DEXTER
Magnitude: 0.75 
Reported by: AMATEUR RADIO

Hail in DALLAS, IOWA
From 10-MAY-05 22:03:00 to 10-MAY-05 22:03:00 (CST)
Location: DE SOTO
Magnitude: 1.75 
Property damage: 10K
Reported by: TRAINED SPOTTER

Hail in MADISON, IOWA
From 10-MAY-05 22:08:00 to 10-MAY-05 22:08:00 (CST)
Location: EARLHAM
Magnitude: 0.88 
Property damage: 2K
Reported by: AMATEUR RADIO

Hail in AUDUBON, IOWA
From 10-MAY-05 22:10:00 to 10-MAY-05 22:10:00 (CST)
Location: BRAYTON
Magnitude: 0.88 
Property damage: 2K
Reported by: LAW ENFORCEMENT

Hail in MADISON, IOWA
From 10-MAY-05 22:25:00 to 10-MAY-05 22:25:00 (CST)
Location: WINTERSET
Magnitude: 0.88 
Property damage: 2K
Reported by: LAW ENFORCEMENT

Hail in CERRO GORDO, IOWA
From 10-MAY-05 22:28:00 to 10-MAY-05 22:28:00 (CST)
Location: MASON CITY
Magnitude: 1.00 
Property damage: 3K
Reported by: GENERAL PUBLIC

Hail in WINNEBAGO, IOWA
From 10-MAY-05 22:30:00 to 10-MAY-05 22:30:00 (CST)
Location: THOMPSON
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Hail in DALLAS, IOWA
From 10-MAY-05 22:30:00 to 10-MAY-05 22:30:00 (CST)
Location: REDFIELD
Magnitude: 1.00 
Property damage: 5K
Reported by: TRAINED SPOTTER

Hail in DALLAS, IOWA
From 10-MAY-05 22:31:00 to 10-MAY-05 22:31:00 (CST)
Location: DE SOTO
Magnitude: 1.00 
Property damage: 3K
Reported by: TRAINED SPOTTER

Hail in POLK, IOWA
From 10-MAY-05 22:58:00 to 10-MAY-05 22:58:00 (CST)
Location: DES MOINES
Magnitude: 0.88 
Property damage: 2K
Reported by: TRAINED SPOTTER

Hail in GUTHRIE, IOWA
From 10-MAY-05 20:47:00 to 10-MAY-05 20:47:00 (CST)
Location: GUTHRIE CENTER
Magnitude: 1.75 
Property damage: 5K
Reported by: TRAINED SPOTTER

Hail in GUTHRIE, IOWA
From 10-MAY-05 20:50:00 to 10-MAY-05 20:50:00 (CST)
Location: PANORA
Magnitude: 0.75 
Reported by: AMATEUR RADIO

Hail in GUTHRIE, IOWA
From 10-MAY-05 21:07:00 to 10-MAY-05 21:22:00 (CST)
Location: STUART
Magnitude: 1.75 
Property damage: 10K
Reported by: TRAINED SPOTTER

Hail in CASS, IOWA
From 10-MAY-05 21:09:00 to 10-MAY-05 21:09:00 (CST)
Location: ATLANTIC ARPT
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Hail in DALLAS, IOWA
From 10-MAY-05 21:13:00 to 10-MAY-05 21:13:00 (CST)
Location: DEXTER
Magnitude: 0.75 
Reported by: AMATEUR RADIO

Hail in DALLAS, IOWA
From 10-MAY-05 21:24:00 to 10-MAY-05 21:24:00 (CST)
Location: DEXTER
Magnitude: 0.75 
Reported by: AMATEUR RADIO

Hail in WINNEBAGO, IOWA
From 10-MAY-05 21:32:00 to 10-MAY-05 21:32:00 (CST)
Location: FOREST CITY
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Hail in WINNEBAGO, IOWA
From 10-MAY-05 21:38:00 to 10-MAY-05 21:38:00 (CST)
Location: FOREST CITY
Magnitude: 1.00 
Property damage: 5K
Reported by: BROADCAST MEDIA

Hail in WINNEBAGO, IOWA
From 10-MAY-05 21:40:00 to 10-MAY-05 21:40:00 (CST)
Location: FOREST CITY
Magnitude: 0.88 
Property damage: 2K
Reported by: BROADCAST MEDIA

Hail in WINNEBAGO, IOWA
From 10-MAY-05 21:43:00 to 10-MAY-05 21:43:00 (CST)
Location: FOREST CITY ARPT
Magnitude: 0.88 
Property damage: 2K
Reported by: TRAINED SPOTTER

Hail in DALLAS, IOWA
From 10-MAY-05 21:46:00 to 10-MAY-05 21:46:00 (CST)
Location: DEXTER
Magnitude: 0.75 
Reported by: AMATEUR RADIO

Hail in DALLAS, IOWA
From 10-MAY-05 21:52:00 to 10-MAY-05 21:52:00 (CST)
Location: DE SOTO
Magnitude: 1.00 
Property damage: 5K
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 10-MAY-05 18:26:00 to 10-MAY-05 18:26:00 (CST)
Location: GRAY
Magnitude: 1.00 
Property damage: 2K
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 10-MAY-05 18:30:00 to 10-MAY-05 18:30:00 (CST)
Location: BRAYTON
Magnitude: 0.88 
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 10-MAY-05 18:32:00 to 10-MAY-05 18:32:00 (CST)
Location: BRAYTON
Magnitude: 1.00 
Property damage: 2K
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 10-MAY-05 18:39:00 to 10-MAY-05 18:39:00 (CST)
Location: AUDUBON
Magnitude: 2.00 
Property damage: 10K
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 10-MAY-05 18:54:00 to 10-MAY-05 18:54:00 (CST)
Location: GRAY
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Hail in CARROLL, IOWA
From 10-MAY-05 18:56:00 to 10-MAY-05 18:56:00 (CST)
Location: MANNING
Magnitude: 0.88 
Property damage: 2K
Reported by: TRAINED SPOTTER

Tornado in AUDUBON, IOWA
From 10-MAY-05 18:58:00 to 10-MAY-05 19:05:00 (CST)
Location: KIMBALLTON
Tornado F-scale: F0
Property damage: 2K
Reported by: TRAINED SPOTTER

Tornado tracked through open fields.

Hail in GUTHRIE, IOWA
From 10-MAY-05 20:24:00 to 10-MAY-05 20:24:00 (CST)
Location: GUTHRIE CENTER ARPT
Magnitude: 0.88 
Property damage: 1K
Reported by: TRAINED SPOTTER

Hail in AUDUBON, IOWA
From 10-MAY-05 20:32:00 to 10-MAY-05 20:32:00 (CST)
Location: EXIRA
Magnitude: 1.00 
Property damage: 2K
Reported by: AMATEUR RADIO

Lightning in HAMILTON, IOWA
From 11-MAY-05 02:00:00 to 11-MAY-05 02:00:00 (CST)
Location: WEBSTER CITY
Property damage: 50K
Reported by: NEWSPAPER